1. Field of the Invention
This invention relates to an apparatus and a method for interpolating image data comprising dot matrix picture elements by a predetermined scale factor and a medium on which an image data interpolation program is recorded.
2. Description of the Prior Art
An image is represented as dot matrix picture elements when treated in a computer, and each picture element is represented by a gradation value. For example, a photograph and computer graphics are sometimes displayed on a screen of the computer by 640-dot picture elements in the horizontal direction and 480-dot picture elements in the vertical direction.
On the other hand, color printers have recently been improved in their performances rapidly and now have a high accurate dot density, for example, 720 dpi. When an original image composed of 640xc3x97480 dots is printed so that a printed image corresponds to the original one in the dots, the printed image becomes smaller than the original one. In this case, images to be printed have various gradation values, and the color printers have different resolutions. Accordingly, the original image data is required to be interpolated between dots before converted to printing image data.
The prior art has provided, as techniques for interpolating the dots, a nearest neighbor interpolation method (hereinafter, xe2x80x9cnearest methodxe2x80x9d) and a cubic convolution interpolation method (hereinafter, xe2x80x9ccubic methodxe2x80x9d). Further, publication No. 6-225140 of a Japanese patent application discloses a technique for providing dot patterns so that an edge takes such an enlarged form as to be smoothed when edge smoothing is performed after dots have been interpolated.
The aforesaid interpolation techniques have the following problems. The nearest and cubic methods have their respective advantages and disadvantages. It is difficult for users to select either method in view of the relation between the interpolation technique and an interpolating scale factor. Further, when either method is selected and applied to an image unsuitable therefor, there is a possibility of a reduction in the quality of interpolation.
In the invention disclosed in the above-mentioned publication No. 6-225140, an interpolating scale factor is inevitably fixed since the dot patterns are previously provided. Accordingly, the interpolation cannot be applied to a case of any scale factor. Further, when color images are interpolated, the number of dot patterns to be previously provided becomes enormous and accordingly cannot previously be prepared.
Therefore, an object of the present invention is to provide an image data interpolation apparatus and method wherein results of optimum interpolation can be obtained for any interpolating scale factor, and a medium on which such an image data interpolation program is recorded.
The present invention provides an image data interpolation apparatus comprising an image data obtaining unit for obtaining image data representing an image as dot-matrix picture elements, a picture element interpolating unit capable of selectively executing one of a plurality of interpolating processes when the image data is interpolated so that the number of constituent picture elements thereof is increased, an interpolating scale factor obtaining unit for obtaining an interpolating scale factor suitable for the image data, and an interpolating process selecting unit for selecting one of the interpolating processes capable of obtaining an optimum result of interpolation according to the interpolating scale factor obtained by the interpolating scale factor obtaining unit and causing the picture element interpolating unit to execute the selected interpolating process.
In the invention thus constituted, the picture element interpolating unit is capable of executing one of the plurality of interpolating processes when interpolation is to be executed so that the number of constituent picture elements of the image data representing the image as dot-matrix picture elements is increased. When the image data obtaining unit obtains image data to be interpolated, the interpolating scale factor obtaining unit obtains the interpolating scale factor for the image data. The interpolating process selecting unit selects one of the interpolating processes capable of obtaining an optimum result of interpolation according to the interpolating scale factor obtained by the interpolating scale factor obtaining unit, causing the picture element interpolating unit to execute the selected interpolating process.
According to the aforesaid invention, the interpolating process to be executed is switched according to the selected interpolating scale factor. Consequently, the image data interpolation apparatus can easily achieve an optimum result of interpolation for the image data.
The technique for selecting one of a plurality of interpolating processes according to an interpolating scale factor should not be limited to a substantial apparatus. It can easily be understood that the technique is functioned as a method. Accordingly, the invention also provides an image data interpolation method comprising the steps of obtaining image data representing an image as dot-matrix picture elements, obtaining an interpolating scale factor suitable for the image data, selecting one of a plurality of interpolating processes capable of obtaining an optimum result of interpolation according to the obtained interpolating scale factor, and executing the selected interpolating process on the image data.
Thus, it is sure that the technique is not limited to a substantial device but is effective as a method.
The aforesaid image data interpolation apparatus may exist independently or may be incorporated into equipment. In other words, the scope of the present invention covers various forms of implementation. Further, the device may be implemented by hardware or software. When the apparatus is implemented by software, the invention applies equally to a medium on which the software is recorded.
As one example, the invention further provides a medium on which an image data interpolation program is recorded, the program causing a computer to execute an interpolating process for image data representing an image as dot-matrix picture elements and obtained by the computer so that the number of constituent picture elements of the image data is increased by a predetermined interpolating scale factor, the program causing the computer to execute the steps of obtaining image data representing an image as dot-matrix picture elements, obtaining an interpolating scale factor suitable for the image data, selecting one of a plurality of interpolating processes capable of obtaining an optimum result of interpolation according to the obtained interpolating scale factor, and executing the selected interpolating process on the image data.
The recording medium may be a magnetic recording medium, a photo-electromagnetic recording medium, any type of recording medium which will be developed in the feature. Further, it can be understood that the medium may be a first or second copy and that a telecommunication line may also be used to supply the program. Further, there is no difference as regards the concept of the invention even if one part is software and another part is hardware, or when it is in such a form that one part is stored on a recording medium which can be read when necessary.